Let the eggs cool and peel and slice them. Dice the tomato. Finely dice the onion. Pluck or chop the parsley (to taste). Put everything in a bowl. The mayonnaise with it. You may not need half the glass. You just have to see that it doesn`t turn out to be mush, but rather remains salad. Then season with salt and pepper.
Let it steep in the refrigerator for about 20 minutes.